JPS63175872A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To form a positive outline image from a positive original image with the one copying process by providing first and second electrifiers. CONSTITUTION:The image of an original is exposed on the surface of an electrostatic latent image carrier to which the electric charge having a certain potential is given by the first electrifier 2, and a DC voltage having the polarity opposite to that of the voltage applied to the first electrifier is applied to the second electrifier 4 and a voltage which has the same polarity as the voltage applied to the first electrifier and is lower than the surface potential of the image part of the electrostatic latent image formed by an image exposure device and is higher than the surface potential of the non-image part is applied to the second electrifier to electrify the electrostatic latent image carrier again and then, the surface potential of the image part of the electrostatic latent image is reduced to the about grid voltage except the outline part. The electrostatic latent image passing the second electrifier is regularly developed with a charged toner having the polarity opposite to that of the voltage applied to the first electrifier. The distance between wires of the grid of the second electrifier 4 is set to <=1mm to prevent omission of the line image part.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic copying apparatus, and more particularly, to an electrophotographic copying apparatus having a function of forming an outline image corresponding to the inner peripheral part of the outline of an original image. .

Conventional Techniques and What's Happening In general, in an image, the contour line is a part with a lot of information, and at the same time, it fully expresses the characteristics of the image, and thus plays an important role in the image. Furthermore, images that have been converted into binary figures by drawing contour lines are easier to identify than normal grayscale images.

Extremely easy to handle in multiple processes such as determination and transmission,
Converting an image into a binary figure by drawing a contour line is extremely effective in terms of image pattern recognition, image correction/enhancement, bandwidth compression, and the like. In addition, for example, by repeating two copies and adding a colored outline around a black pattern to make it more conspicuous, or by painting one pattern in different colors to create patterns with different colors, so-called painting is possible. It is also useful when preparing logical patterns.

By the way, conventional methods for forming contour images of this type include:
The present applicant has already developed a one-component toner developing method in which an electrostatic latent image is developed with a conductive toner, which has a potential intermediate between the maximum and minimum surface potentials of the member to be developed, and By applying a DC bias of opposite polarity to the latent image charge between the member to be developed and the conductive toner carrier,
proposed a method characterized by extracting the contour line of an electrostatic latent image on a member to be developed (Japanese Patent Application Laid-Open No. 51-134635).
(see publication).

However, in this method, the contour formed as a silent latent image is a negative image, and the conductive toner adheres to areas with a large potential difference based on the potential difference on the surface of the electrostatic latent image carrier, that is, areas other than the contour line. Therefore, the developed image is obtained only as a negative image. Normally, the required contour image is a positive image (black image), so in order to create a positive image, the negative contour image obtained by this method must be copied again using reversal development. It has points.

Therefore, the present invention provides an electrophotographic copying method that can form a positive outline image from a positive original image in a single copying process, and can also reproduce a line image as a line image without hollowing out the outline image. The purpose is to provide equipment.

In order to achieve an objective that is more than a means for solving the problems, the electrophotographic copying apparatus according to the present invention includes: (1) a first charging device that applies a constant electric charge to the surface of the electrostatic latent image carrier; (j) an image exposure device that exposes an image of a document onto the surface of the electrostatic latent image carrier fully charged by the first charging device; (i) an electrostatic latent image formed by the image exposure device; An alternating voltage or a direct current WEE of opposite polarity to the voltage applied to the first charging device is applied to the surface of the electrostatic latent image carrier, and a voltage same as the voltage applied to the first charging device is applied to the grid. A voltage that is polar and lower than the surface potential of the image area of the electrostatic latent image formed by the image exposure device and higher than the surface potential of the non-image area is applied, and the distance between the wires of the grid is 1 mm or less. (iv) a developing device that develops the electrostatic latent image that has passed through the second charging device with a charged toner having a polarity opposite to the voltage applied to the first charging device; It is characterized by having

In an electrophotographic copying apparatus having the above-described configuration, first, an image of a document is exposed onto the surface of an electrostatic latent image carrier that is charged with a constant potential by a first charging device (see (a) in FIG. 3). )
After that, for example, a DC voltage of opposite polarity to the voltage applied to the first charging device is applied to the second charging device, and a DC voltage of the same polarity as the voltage applied to the first charging device is applied to the grid. Recharging is performed while applying a voltage that is lower than the surface potential of the image area of the electrostatic latent image formed by the image exposure device and higher than the surface potential of the non-image area. As a result, the surface potential of the electrostatic latent image area is reduced to approximately the grid voltage, leaving the contour area (see (b) in FIG. 3).

Next, the electrostatic latent image that has passed through the second charging device is regularly developed with charged toner having a polarity opposite to that of the voltage applied to the first charging device. As a result, the charged toner adheres to the contour of the electrostatic latent image portion left at a high potential, and the contour image is developed as a positive image (see (e) in FIG. 3).

In addition, in the second charging device, since the distance between the wires of the grid is set to 1 mm or less, the ion flow from the grid toward the surface of the electrostatic latent image carrier is restricted to some extent, and the line image portion is hollow. is prevented.

Embodiment FIG. 1 schematically shows an embodiment of an electrophotographic copying apparatus, in which the electrophotographic photosensitive drum (1) is of a well-known type having a photoconductive layer on its outer peripheral surface, and can be rotated in the direction of arrow (a). and
The members and devices described below are installed around it.

The charger (2) functions as a first charging device that applies a constant potential charge (positive charge in this embodiment) to the surface of the photoreceptor drum (1), and connects the charge wire to the charger (2). is connected to a power source (21).

The image exposure device (3) applies light to the document placed on the document platen glass (34) and uses a well-known slit exposure method to form an electrostatic latent image on the surface of the photoreceptor drum (1) corresponding to the document image. It is used only to form an image, and is composed of an exposure lamp (31), a mirror (not shown), a lens (33), etc., and a power source (32) is connected to the exposure lamp (31).

The scorotron charger (4) is connected to the exposure device 3.
) functions as a second charging device for recharging the surface of the photoreceptor drum (1) on which an electrostatic latent image has been formed.A power source (41) is connected to the chill wire, and the grid A power source (43) is connected to (42). The charge wire is connected from the power source (41) to the charger (2).
) is applied so that a voltage of opposite polarity is applied. Also, the grid (42) has a power supply (43)
A voltage of the same polarity as the voltage applied to the charger (2) from the electrostatic latent image area, which is sufficiently lower than the surface potential of the image area and slightly higher than the surface potential of the non-image area, is applied. .

The developing device (5) is a well-known magnetic brush type device that includes a developing sleeve (51) that includes a built-in magnetic roller (52) with N and S poles magnetized around its periphery, and also functions as a developing electrode. A power source (53) for developing bias is connected to the developing sleeve (51). The developer is made of a mixture of a magnetic carrier and an insulating toner, which are charged to opposite polarities by frictional charging, and the insulating toner is charged to a polarity opposite to that of the charger (2). Here, if the insulating toner does not have magnetism, the developing sleeve (
A developing bias which is slightly higher than the grid voltage and has the same polarity as the charger (2) is applied from the power supply (53) to the developing bias (51). On the other hand, when the insulating toner has magnetism, a developing bias lower than the grid voltage and on which an alternating current voltage is superimposed is applied to the developing sleeve (51). However, in this case, only insulating toner can be used. Furthermore, it is not necessary to superimpose an alternating current voltage on the developing bias.

The transfer charger (6) applies an electric field from the back side to the copy paper (10) being conveyed in the direction of arrow (b), and the developing device (5) applies an electric field to the surface of the photoreceptor drum (1). It is used to transfer the formed toner image onto the copy paper (10), and a voltage having a polarity opposite to that of the insulating toner is applied to the charge wire from a power source (61).

The separation charger (7) applies an alternating current electric field to the copy paper immediately after transfer to remove static electricity from the copy paper (10) and separate it from the surface of the photoreceptor drum (1). An alternating current voltage is applied to the wire from a power source (71).

The cleaning device (8) uses a blade method to remove toner remaining on the surface of the photoreceptor drum (1).

The eraser lamp (9) is used to remove charges remaining on the surface of the photoreceptor drum (1) by irradiating light in preparation for the next copying process.

The control of this copying apparatus is mainly performed by a microcomputer (CPU), and each of the power supplies (32) and <41
).

The on/off control of (43>, (52), etc.), the voltage switching control of the power source (32), etc. are also processed by the microcomputer (CPU).

Here, the polarity and voltage of each charger etc. in this example will be shown.

[I] When using non-magnetic insulating toner Charger [Power source (21)] Positive polarity +5.5kV Scorotron charger [iff<4x)] Negative polarity -6, OkV Grid [IE source (43) Positive polarity +220■ Development bias [power supply (53)] Positive polarity +250v Transfer charger ct source (61st) Positive polarity +5.5kV Non-magnetic insulating toner Negative polarity [II] When using magnetic insulating toner Charger [power supply (21) ) Positive polarity + 5.5kV Scorotron charger [tm (4t) ] Negative polarity -
6, OkV Grid [Electric power (43) positive polarity + 220v Development bias [power supply (53) positive polarity (DC) + 170V (AC) 350Vrms, 1kHz Development start potential +250v Magnetic insulating toner negative polarity Please note that these polarities Regarding, everything may be reversed,
Of course, the voltage value, exposure light amount, etc. are merely examples.

The method for forming an outline image using the copying apparatus described above will be explained step by step.

(i> First charging step The charger (2) applies a constant potential charge to the surface of the photoreceptor drum (1). As a result, in this example, the surface potential of the photoreceptor drum (1) is It becomes 600V.

(i) Exposure step A positive original image is exposed to slit light on the surface of the photoreceptor drum (1) charged to a potential of +600V to form an electrostatic latent image. In this case, as shown in (a) in Figure 3, the charge of the portion corresponding to the image areas (A) and (B) is +600V.
The electric charge of the portion corresponding to the non-image area is reduced to about +90V by light irradiation.

(i) Second charging step The surface of the photoreceptor drum (1) on which the electrostatic latent image has been formed is charged with a scorotron charger (4) to which a voltage of -6,000 kV is applied from the power source (41). Recharge.

At this time, the grid (42) receives +2 from the power supply (43).
A voltage of 20v is applied. The voltage applied to the scorotron charger (4) is of opposite polarity to the voltage applied to the charging charger (2). Also, grid (42)
The voltage applied to the electrostatic latent image portions (A), (B) has the same polarity as the voltage applied to the charged charger 2).
) is sufficiently lower than the surface potential of the non-image area (<+600V) and slightly higher than the surface potential of the non-image area (+90V).

Electric lines of force shown by arrows in FIG. 2 are formed between the surface of the photosensitive drum (1) and the grid (42).

Then, the negative polarity ions generated from the charge wire are subjected to a transport force along the lines of electric force. In this case, the electric lines of force that direct negative ions toward the surface of the photoreceptor drum (1) near the grid (42) are located at a portion ( Therefore, the negative ions reach only the central part of the surface image area (A) as shown by the arrow →, eliminate the charge in the area they reach, and remove the charge at the grid voltage ( +220V) (see (b) in Figure 3)
.

That is, in terms of the surface potential of the photoreceptor drum (1), as shown in FIG. 3(b), the surface potential (Vi) of the non-image area of the electrostatic latent image is left as a low potential area of approximately +90V. ,
Contour inner side of surface image portions (A) and (B) <A').

(Bo) is the initial surface potential with a constant width of approximately +60
It remains as a high potential part (Vo) of 0V and also remains as a surface image part (
The center part of A) is almost the grid voltage (Vg! +220
Note that the surface potential (vO) of the inner side of the line image area (Bo) almost never decreases, but the width of the charge is lower than that of the line image area (B). It narrows down a bit.

In other words, the image area (A) in this second charging step.

This means that the contour shown in (B) is formed as a positive electrostatic latent image.

(iv) Developing step In the second charging step, the electrostatic latent image formed as a positive image of the contour portion is developed by a developing device (5). If the insulating toner does not have magnetism, the developing sleeve (51
) is applied with a developing voltage of +250V. This developing bias is applied to the central part of the electrostatic latent image area (A) where the surface potential has decreased in the second charging process (and of course to the non-image area).
In order to prevent toner from adhering and fogging, the voltage t applied to the charger (2) has the same polarity as JE, is slightly higher than the grid voltage (vg: 220V), and is approximately equal to the grid voltage (Vg). The voltage (vb) is slightly higher than the potential (Vo') at the center of the plane image area (A), which has decreased to around the same value.

On the other hand, if the insulating toner has magnetism, the developing sleeve (51) has AC350V, 1kHz and +17V.
0V (7) Developing bias is applied. WEE (Vb)4i of this developing bias, the grid voltage (Vg:
+220V) and lower than the potential (Vo') of the central part of the surface image area (A), which has decreased to a value approximately equal to the grid voltage (Vg). In this case, since there is a threshold value due to magnetic binding force, development starts when the surface potential is around 250V. For this reason, the electrostatic latent image reduced in the second charging process is applied to the central part of the image area (A) (of course also to the non-image area).
There is no chance that toner will stick to it and cause it to fog.

In this way, the negatively charged insulating toner is applied to the high potential area (vO) of the photoreceptor drum (1), that is, the image area (A).

The toner image adheres to the inside parts (A') and (B') of the contour line in (B), and a so-called "inner edging" toner image is formed by regular development.

This toner image is then transferred onto the copy paper (10) by negative discharge from the transfer charger (6), and is formed as a copy image via a fixing device (not shown).

By the way, the present inventors conducted a detailed experimental study on various conditions of the Suflotron charger (4), and found that the condition of the contour image, especially the density of the contour line, was affected by the grid (42) and the photoreceptor. The closest distance (dg) to the surface of the drum (1) and the distance between the wires of the grid (42) (dv
) (see Figure 4) was found to be important.

At the same time, the grid (
It has also been found that the value of the distance between wires (dw) in 42) is important.

That is, regarding the former, when the distance between the wires (dw) is large and the distance between the grid and the surface of the photoreceptor (dg) is small, a good contour image cannot be formed.

Regarding the latter, when the distance between the wires (dw) is large, even if the line image is a line image, the center part becomes white and becomes a thin outline image, and the line image cannot be reproduced as a line image.

Here, the above phenomenon will be explained in more detail based on specific experimental results.

The grid (42) used in the experiments by the present inventors was manufactured by etching a stainless steel plate with a thickness of 0.1 mm, as shown in the plan view in FIG. .1mm. The distance between wires (dw) is the shortest distance between adjacent wires, ranging from 0.30 mm to 2.
An experiment was conducted using a grid in which (dw) was changed in five steps up to 0.05 mm.

In Figure 5, which shows the experimental results, the ◯ mark indicates a condition under which a good contour image was formed, and the x mark indicates a condition under which only a thin contour image with low density was formed. The Δ mark is the condition under which the intermediate contour image was formed. The straight line shown in the figure is the line of (dg) = (d%#), and (dg)
It was found that a good contour image was formed under the condition of > (dw). That is, in the setting of Sufrotron charger (4>), (dg)>
By determining the shape and position of the grid (42) so as to satisfy the condition (dw), a good high-density contour image can be obtained.

By the way, in order to obtain a high-density contour image, (dg)>(
The reason why the condition dw) is necessary can be considered as follows.

As explained in the copying process, the outline image is formed because the lines of electric force from the end of the electrostatic latent image area do not go toward the photosensitive drum (1
) side. The degree of this is proportional to the distance (dg) between the grid and the photoreceptor surface, and (dg
) is larger, a better contour image is formed. On the other hand, when the wire distance (dw) of the grid (42) of the Suflotron charger (4) becomes wider, the influence of the charge wire of the Suflotron charger (4) also appears on the electrostatic latent image on the photoreceptor. The Sufrotron effect car decreases, and more static electricity is removed than necessary. That is, the distance between the wires (d
When w) becomes large, it is difficult to form a good contour image.

Therefore, as a condition for the combination of the above two effects, for example, as (dw) becomes larger and it becomes difficult to form a good contour image, (dg) is increased to complement each other. It seems that the condition (dw) < (dg) occurred.

Similarly, FIG. 6 shows experimental results regarding the reproduction state of line images.

In the figure, the ○ mark indicates a condition in which a line image is reproduced as a line image, and the X mark indicates a condition in which even though it is a line image, the central part is left white, resulting in a thin outline image. (dv)51.0
It has been found that a line image can be reproduced as a line image under the condition of mm. In other words, when there is a desire to reproduce not only a contour image but also a surface image as a contour image and a line image as a line image, the grid (4) is
The above requirement can be met by setting the wire distance (dw) of 2) to 51.0 mm.

In addition, in the above embodiment, the distance between the wires (dw) is 0.
．． A grid (42) of 65 mcn was used, and the distance between the grid and the surface of the photoreceptor (dg) was set to 1.5 mm, which clearly satisfied both of the above conditions and was described in the explanation of the above example. In this way, a good contour image is formed and a line image is reproduced as a line image.

By the way, the reason why the condition of (dw) 51.0 mm is necessary to reproduce a line image as a line image in a contour image is presumed as follows.

As the distance between wires of the grid (dw) increases, (d
When v) is small, ions that have been blocked by the grid come out between the grid and the surface of the photoreceptor drum, and the amount of ions there increases.

When the amount of ions increases, there are ions that adhere to the electrostatic latent image on the surface of the photoreceptor other than those along the lines of electric force. Since the electric field is strongest in the center of the line image, these ions tend to adhere, and if they do, the charge cannot be removed and the center appears white.

In each of the above embodiments, the first charging device (
Although a DC voltage having a polarity opposite to that applied in step 2) is applied, an alternating voltage may also be applied. In this case, in the second charging step, the surface potential of the electrostatic latent image area is reduced to approximately the grid voltage, leaving the area inside the contour line, and the surface potential of the non-image area is decreasing, leaving the area near the image area. The voltage will rise almost to the grid voltage.

In addition, since the development by the development device (5) is based on the regular development method, the Sufrotron charger (4)
If the second charging step is not performed, the positive electrostatic latent image formed in the image exposure step can be developed as normal regular development, and a positive image corresponding to the original image can be obtained. This turns on the Sufrotron charger (4),
It can be easily controlled by switching off.

Effects of the Invention As is clear from the above explanation, according to the present invention, a second charging device having a grid is provided between the image exposure device and the developing device, and the voltage applied to the second charging device is is an alternating voltage or a direct current voltage of opposite polarity to the voltage applied to the first charging device, and the voltage applied to the grid is set to be an alternating voltage or a direct current voltage of opposite polarity to the voltage applied to the first charging device, and the voltage applied to the grid is set to an image exposure device Because the voltage value was set lower than the surface potential of the image area of the electrostatic latent image formed and higher than the surface potential of the non-image area, the outline of the original image remained as a high potential area on the surface of the electrostatic latent image carrier. A positive electrostatic latent image is formed, and since regular development is carried out by storing a developer containing charged toner with a polarity opposite to that of the electrostatic latent image in the developing device, in this regular development, the electrostatic latent image is The toner adheres to the contour portion of the document image, which is the high potential portion of the latent image, and a positive contour image can be obtained. Moreover, since the distance between the wires of the grid is set to 1 mm or less, the ion flow from the grid to the surface of the electrostatic latent image carrier is restricted to some extent, preventing hollows in the line image area and converting the line image into a line in the contour image. It can be accurately reproduced as an image.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a copying apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram of electric lines of force produced by a second charging device, and FIG. 3 is a diagram of electrostatic latent images in each image forming process. Graph showing the potential, Figure 4 is a plan view of the grid, Figures 5 and 6 are the distance between wires (dw) and the distance between grid and photoreceptor surface (dg).
2 is a graph showing reproducibility based on . (1)... Electrophotographic photosensitive drum, (2)... Charger, (3)... Image exposure device, (4)...
Sufrotron charger, (42>...grid,
(5>...Developing device, (51)...Developing sleeve,
(dg)...Distance between grid and photoreceptor surface, (dw)
...Distance between wires.

Claims (1)

[Claims] 1. A first method for applying a constant potential charge to the surface of the electrostatic latent image carrier.
a charging device; an image exposure device that exposes an image of a document onto the surface of the electrostatic latent image carrier charged by the first charging device; and an electrostatic latent image formed by the image exposure device. An alternating current voltage or a DC voltage of opposite polarity to the voltage applied to the first charging device is applied to the surface of the electrostatic latent image carrier, and a voltage having the same polarity as the voltage applied to the first charging device is applied to the grid. A second method in which a voltage lower than the surface potential of the image area of the electrostatic latent image formed by the image exposure device and higher than the surface potential of the non-image area is applied, and the distance between the wires of the grid is 1 mm or less. a charging device; and a developing device that develops the electrostatic latent image that has passed through the second charging device with a charged toner having a polarity opposite to that of the voltage applied to the first charging device. Characteristic electrophotographic copying device.